Product manual

CDA 7 5630 Product Manual
3-6 77 A1 69UP Rev00
3.2 Elements of a CDA 7 I/O Operation
All I/O operations require a certain response time. An I/O request begins with the
application issuing an I/O command and ends when the transfer completes. The
time lapse from I/O request to transfer completion is the I/O response time.
3.2.1 I/O Response Time
The I/O response time can be divided into a host queuing time, a command connect
time, a disconnect time, and a data connect time, as shown in the following figure.
HOST
QUEUING
TIME
COMMAND
CONNECT
TIME
DISCONNECT
TIME
DATA
CONNECT
TIME
DEVICE SERVICE TIME
I/O RESPONSE TIME
Figure 3-4. I/O Response Time
The Host Queuing Time is the time the request is in the host queue before it is
dispatched on the SCSI bus.
The Command Connect Time is the length of time the channel is transferring a
SCSI command.
The Disconnect Time is the length of time involving device seek and latency. At
this time the SCSI bus can be used by other devices.
NOTE:
In case of a cache hit in an I/O request, the Disconnect Time requirement is
eliminated.
The Data Connect Time is the length of time the channel is transferring data.
There are four basic types of CDA 7 I/O operations:
• Read Hit
• Read Miss
• Fast Write
• Delayed Fast Write